Gathered tubular foodstuff wrapping based on cellulose

ABSTRACT

The invention relates to a stick of a tubular food casing based on cellulose. The casing is produced by the NMMO process. The stick is particularly stable and is thus suited for automatic filling devices such as those used for producing cooked or boiled sausages.

[0001] The invention relates to a shirred tubular food casing based on cellulose. It is particularly suitable for producing small sausages.

[0002] Food casings, especially sausage casings, are frequently offered in a form in which in each case about 15 to 50 m of the casing are compacted to sticks about 20 to 60 cm long. Shirring the synthetic skin has long been known and it is described repeatedly in the general specialist literature as in the patent literature (for example in the monograph by G. Effenberger, Wursthüllen—Kunstdarm [Sausage casings—synthetic skins], H. Holzmann Verlag GmbH & Co. KG, Bad Wörishofen, 2nd edition [1991] pp. 58-60). It is performed on shirring machines. Before shirring, the casing is laid flat and rolled up. It is then taken off from the roll, inflated and pushed onto the shirring mandrel of the shirring machine. The outer diameter of the shirring mandrel determines here the inner diameter of the stick to be produced. Shirring represents a high stress for the casing. Immediately before or during shirring, it is therefore customarily sprayed or wetted with water and/or oil from the inside, from the outside or from both sides, in order to make it more supple. This prevents cracks forming at the shirring pleats. The shirring tools themselves can be of quite different designs. Those which are known are, for example, shirring wheels, which can be smooth or toothed on the outside, and in addition also circulating belts. When the desired number of meters has been shirred, the casing is cut. The stick thus produced is intended to be as dimensionally stable and self-supporting as possible. Nevertheless, for storage and transport, it is frequently provided with an overpacking (generally a net or a film). Finally, casings are also known which are shirred onto a dimensionally stable tube. The stick is deshirred again on stuffing with sausage emulsion. Frequently in this case, a number of sticks are placed into a storage holder from which individual sticks are then automatically removed and pushed onto the stuffing horn of the fast-running stuffing machine. It is of critical importance here that the stick does not break, especially not if it has been watered. Otherwise a fault occurs in the outlet, which must be removed by hand in a complex manner.

[0003] The portioning of the sausages and closing or tying of the sausage ends which are necessary after stuffing customarily likewise proceed automatically. In this manner, inter alia, small sausages are also produced. The small-sausage emulsion is portioned in this case via the stuffing machine pump. On each interruption of the conveying operation, the appropriate small sausage length is produced by twisting off. The entire operation proceeds fully automatically at high speed. The chain of small sausages thus produced is, also mechanically, suspended on a suitable frame on which the small sausages are then introduced directly into the further treatment stages. With these scalded-emulsion sausages, the casing is used as stuffing and production aid and is mechanically peeled off after cooking or scalding (if appropriate also smoking) and chilling the small sausages before packaging in pouches, jars or tins.

[0004] Tubular food casings based on cellulose have previously been produced predominantly by the viscose process. In this process a cellulose xanthogenate solution (=viscose) is extruded through a ring die under pressure. The cellulose is then regenerated from the viscose in various precipitation and washing baths. The first precipitation bath is generally an aqueous sodium sulfate/sulfuric acid solution (the Müller bath). For precipitation, aqueous ammonium sulfate/sodium sulfate/sulfuric acid baths are also used. The tube of regenerated cellulose is then washed, if appropriate treated with a plasticizer (glycerol) provided internally and/or externally with an impregnation (for example for easier peelability), dried to the intended final mixture content and rolled up. The rolled product can then be shirred in sections, as described. The mechanical strength of unwatered and watered sticks of tubular cellulose casings which are produced by the viscose process, however, leaves much to be desired.

[0005] An object was therefore to improve the mechanical stability of shirred sticks of tubular cellulose casings. This object was achieved by the means that, instead of the cellulose casings produced by the viscose process, casings produced by the N-methylmorpholine N-oxide (NMMO) process are used for shirring.

[0006] The present invention therefore relates to a stick of a tubular food casing based on cellulose which is characterized in that the casing is produced by the NMMO process.

[0007] Preferably, the casing (in the unshirred state) has a nominal caliber of 14 to 50 mm, preferably 16 to 25 mm. It is then particularly suitable as a peelable skin, in particular in the production of small sausages. A stick comprises in this case about 30 to 70 m, preferably about 40 to 60 m, of the casing.

[0008] The production of (unshirred) tubular cellulose casings by the NMMO process is known per se (WO 97/31970). This exploits the fact that cellulose is soluble in oxides of tertiary amines without chemical change, that is to say without derivatization. N-methylmorpholine N-oxide (termed NMMO hereinafter) has proved to be a particularly suitable oxide of a tertiary amine. A great advantage of this process is that it is technically less complex and less environmentally hazardous (in particular the carbon disulfide required in the viscose process can be avoided). To produce the cellulose solution, pulp (for example from wood or cotton) is mashed at room temperature in a 60% strength by weight N-methyl-morpholine N-oxide solution with stirring. Under increasing temperature and reduced pressure, water is distilled off until the residue consists virtually only of cellulose and NMMO monohydrate. The solvent then consists of 87.7% by weight NMMO and the remainder water. The cellulose is completely dissolved therein at a temperature of about 90 to 105° C. Under stirring and heating at reduced pressure, water is then further removed so that in the spinning solution the solvent for the cellulose consists of 90.5 to 92.5% by weight NMMO and 9.5 to 7.5% by weight water. The cellulose content is 6 to 15% by weight, based on the total weight of the spinning solution. A further advantage of the NMMO process is that the length of the cellulose chains remains virtually unchanged (a mean degree of polymerization DP of 400 to 650 is customary). In the viscose process, in contrast, a marked chain degradation takes place. To set particular properties of the casing, it can be expedient to mix the spinning solution with other components. Suitable components are synthetic polymers or copolymers and sugar esters. They act primarily as permanent (“primary”) plasticizers. In addition they decrease the tendency to crystallization of the cellulose. The content of these additional components can be up to 25% by weight, based on the weight of the dry cellulose. Generally, the content of these components, however, is no more than about 1 to 20% by weight.

[0009] The NMMO/cellulose solution is then extruded (“spun”) downward using an annular die. The temperature of the spinning solution in the annular die is preferably about 85 to 105° C. The annular gap generally has a width of 0.1 to 2.0 mm, preferably 0.2 to 2.0 mm. The width must be appropriate here to the “warpage” (quotient of exit velocity and take-off velocity).

[0010] The primary tube produced in the extrusion is then transversely stretched in the air section between annular die and surface of the precipitation bath. The air section in which the blow molding takes place is preferably 1 to 50 cm, particularly preferably 2.5 to 20 cm. It is also dependent on the diameter (caliber) of the tubular film after blow molding. The blow molding is effected by compressed air or other gases at an appropriate pressure which pass into the interior of the tube through orifices in the die body. Stretching in the transverse direction considerably increases the transverse strength of the tube. After entry into the spinning bath, the spinning bath solution also penetrates into the interior of the cellulose tube via appropriate apparatuses in the die body. As a result the tube solidifies more rapidly, simultaneously the insides of the tube are prevented from sticking together.

[0011] The spinning bath itself is an NMMO-containing aqueous solution. This solution contains about 10 to 20% by weight NMMO. The NMMO can be recovered and reused virtually quantitatively from the precipitation bath. Used aqueous NMMO solutions may be purified, for example, by ion-exchange columns. The water can be taken off under reduced pressure until the NMMO concentration has reached 60% by weight. This NMMO solution may be used again to produce spinning solution.

[0012] For further solidification, it is expedient to pass the laid-flat tube through still more NMMO-containing precipitation vats. If the NMMO content in the precipitation vat is still about 10-20% by weight, it decreases in the following vats. The temperature increases from vat to vat and in the last vat reaches about 70 to 80° C. The precipitation section is customarily followed with further vats filled with water at 40 to 60° C. in which the last traces of NMMO are washed out of the tube. A further plasticizer vat can follow this. It contains an aqueous solution of a plasticizer for cellulose. Suitable plasticizers are particularly polyols and polyglycols, particularly glycerol. The aqueous solution generally contains about 5 to 30% by weight, preferably 6 to 15% by weight, of the plasticizer or of the mixture of various plasticizers. The temperature in the plasticizer vat is customarily between 20 and 80° C., preferably between 30 and 70° C. The tubes are then passed through a dryer in the inflated state, hot-air dryers having proved particularly suitable. Expediently, drying is performed under decreasing temperature (from about 150° C. at the inlet to about 80° C. at the dryer outlet). During drying the swelling value decreases to 130 to 180%, preferably 140 to 170%, depending on drying conditions and glycerol content. During drying the tube is preferably inflated to the original caliber in order to maintain unchanged the degree of transverse orientation once it is achieved.

[0013] After it leaves the dryer the tube is wetted again to a water content of 8 to 20% by weight, preferably 16 to 18% by weight, in each case based on the total weight of the tube. Then, using a pinch-roll pair, it can be laid flat and wound up. Depending on the intended application, the casings can, furthermore, be provided on the inside and/or outside with an impregnation or coating, for example a liquid smoke impregnation, a finished further increased stick stability or an easy-peel internal preparation.

[0014] In order to improve the slidability of the sticks on the stuffing horn and to ensure that the casing can be removed during the later peeling operation without damage to the skin formed on the small sausages, it is proved to be expedient to provide the casings on the inside with an impregnation or coating. This impregnation or coating can be applied before the drying operation or during shirring via the shirring mandrel. Known coatings are, for example, coating with water-soluble cellulose ethers (U.S. Pat. No. 3,898,348), with mixtures of lecithin and alginate, chitosan and/or casein (EP-A 502 431=U.S. Pat. No. 5,358,784), with mixtures of anionic and nonionic water-soluble cellulose ethers and lubricants (EP-A 180 207) or with mixtures of lecithin and polytetrafluoroethylene (EP-A 635 213).

[0015] The casing compacted to form a stick must already be provided with a closure at one end so that the stuffing material does not pass onto the stuffing bench and contaminate the following small sausage chain. The closure must be constructed in such a manner that it prevents the outlet of sausage emulsion but does not prevent air egress, since otherwise the pressure equilibration in the interior would be impeded. When additional separate closure materials are used, such as clips or clamps of plastic or metal there is always the risk that these will pass into the sausage interior together with the emulsion. It is therefore advantageous if the closure is formed by twisting or knotting from the casing material itself (DE-C 12 97 508, DE-B 15 32 029, DE-C 23 17 867; EP-A 129 100).

[0016] Frequently the end closure is produced by pulling out a short piece of the stick using special tongs and pushing it back into the stick interior after short twisting. Another possibility is to use a specially shaped striking pin to deform the final millimeters of the stick and simultaneously push it into its internal bore.

[0017] The cellulose casings produced by the NMMO process can be shirred by processes which are known per se to those skilled in the art. The above described effect of the improved cohesion of the stick is not dependent on a defined shirring process. Suitable processes for shirring are described, for example, in DE-B 12 68 011, DE-B 16 32 137, DE-C 16 32 139, DE-A 22 31 144, DE-A 22 31 145 and DE-A 22 36 600.

[0018] In a more detailed study it has been found that the cellulose casings produced by this process differ in their structure and properties from the previously known casings made of regenerated cellulose. However, it was surprising that these differences are still significantly noticeable in the shirred sticks.

[0019] In order to clarify the differences in the shirred sticks, the surface structure of the casings was studied. It was found that there is a significant difference. Thus casings produced by the NMMO process have a significantly smoother surface than those made by the viscose process. The difference is clearly visible in images which are obtainable using a scanning atomic force microscope (AFM).

[0020]FIG. 1 shows an AFM image of the surface of a watered regenerated cellulose tube produced by the viscose process (using a sodium sulfate/sulfuric acid precipitation bath). The X and Y axes are each divided into 20 micrometer intervals, and the Z axis, in contrast, into 500 nanometer (=0.5 micrometer) intervals (likewise in FIG. 2). The relief is therefore shown exaggeratedly. The difference between the highest and lowest points of the surface is more than 1 000 nm.

[0021]FIG. 2 shows an AFM image of the surface of a watered regenerated cellulose tube made by the NMMO process. The surface is virtually flat. Only isolated elevations are visible. The difference between the highest and lowest points of the surface is significantly less than 500 nm.

[0022] If an aqueous ammonium sulfate/sodium sulfate/sulfuric acid precipitation bath is used in a viscose process instead of the Müller bath, the surface roughness then increases still further. Casings produced using this process variant (obtainable, for example, from Trificel, Brazil) result in shirred sticks having particularly lower mechanical stability. The sticks broke when they were loaded with a weight of 340 g or more. The cellulose casings produced by the viscose process using Müller bath as precipitation bath resulted in sticks having a breaking strength of 600 to about 1 100 g. The inventive sticks, in contrast, with the same type of shirring may be loaded at up to 1 600 g, generally 1 200 to 1 500 g, before they break (see under example 1 for a measurement method for determining breaking strength). The increased stability of the inventive shirred sticks is presumably due to the significantly smoother casing surface which allows the shirring pleats to cohere more strongly.

[0023] The arithmetical mean roughness value R_(a), determined in accordance with DIN 4768, is, for the casings produced by the NMMO process, in the range of about 5 to 14 nm, and in contrast in the casings produced by the viscose process, in the range of 70 to 140 nm.

[0024] In addition, light microscopy images show that the casings obtained in the NMMO process have membranes of regenerated cellulose having a significantly higher density. This leads to a higher strength of the casings or permits a reduced wall thickness for the same strength.

[0025] The smoother surface finally also leads to the fact that the casing may be peeled off more readily. The easy peel preparation customarily applied to the inside of the casing can therefore be decreased or even omitted entirely.

[0026] Finally, the electrokinetic potential (zeta potential) of the casing was also determined. This parameter describes the charge conditions at the interface between a membrane and a liquid phase. Conclusions may be drawn therefrom as to the nature and properties of the surface. Furthermore, it provides information on how the electrolyte and its pH act on the surface. In aqueous media, an electric charge on the membrane surface is observed which is caused by dissociation of functional groups of polymers at the surface of the membrane or specific adsorption of ions from electrolyte solutions. The resultant polarity of the polymer material is responsible for the development of an electrical double layer. The potential of this electrical double layer cannot be measured directly. Therefore, the zeta potential is used to characterize the electrical properties. The potential builds up as soon as the membrane surface having groups that can dissociate and the electrolyte solution move tangentially to one another. The potential corresponds to the net charge density of the membrane surface. The Helmholtz-Smoluchowski equation to describe the zeta potential is as follows: $\zeta = \frac{4\pi \quad \eta \quad \kappa \quad E_{s}}{ɛ_{0}\quad D\quad \Delta \quad P}$

[0027] where

[0028] ζ is the zeta potential [V],

[0029] E_(s) is the streaming potential [V],

[0030] κ is the specific conductivity [Ω⁻¹·cm⁻¹],

[0031] η is the dynamic viscosity [Pa·s],

[0032] ε₀ is the influence constant [C·V⁻¹·cm⁻¹],

[0033] ΔP is the pressure difference [Pa] and

[0034] D is the dielectric constant.

[0035] For the cellulose casings produced by the NMMO process, the zeta potential in the pH range from 6 to 10.5 was about −5 to −25 mV. In the pH range from 3.5 to 5.5, it was about +18 to −15 mV.

[0036] The inventive shirred stick is particularly suitable for processing on fast-running stuffing machines. The above described production faults due to broken sticks virtually no longer occur using it. The sticks may be deshirred without problem on the stuffing horn and stuffed with sausage emulsion. The inventive sticks are particularly suitable in the production of cooked-meat sausages and scalded-emulsion sausages, especially of small sausages. The casing is removed from the small sausages after scalding in a known manner on automatic peeling apparatuses.

[0037] The examples below serve to illustrate the invention. Percentages are percentages by weight, unless stated otherwise.

EXAMPLE 1

[0038] A cellulose gel tube of caliber 18 mm was produced by the amine oxide process and plasticized with glycerol. Immediately before drying, at the inlet of the drying channel the tube was impregnated with a solution of 1.0% carboxymethyl cellulose, 1.0% sorbitan trioleate, 0.5% mixture of mono- and diglycerides and 97.5% water

[0039] by a method known as bubble coating. The impregnation facilitates the later peeling process (“easy peel” impregnation). Before entry into the drying channel, there is a pinch-roll pair which retains the excess of impregnating solution.

[0040] In the dryer, the tube was dried in the inflated state firstly to a moisture of 7 to 8%, then, by spraying with water the tube was brought to 16 to 18% moisture content and rolled up. The intermediate storage was performed in a climatically controlled chamber. In the subsequent shirring, the tube was taken off from the roll and in sections, each of about 50 m in length, was formed into a stick about 40 cm long by a known shirring process with application of paraffin oil. The stick withstood a load of 1 500 g.

[0041] The breaking strength was determined by mounting the stick horizontally so that a 15 cm long piece remained without support. Over the center of this piece was then placed a wire bow (diameter of the wire about 2 mm) which was loaded with an increasing number of weights until the stick broke. The weight which the stick withstood was measured. This measurement method was also applied in the following examples.

[0042] In a subsequent step the stick was then provided with an end closure. For this the sticks were individually pushed into an appropriately shaped apparatus and the last pleats were pressed with mechanical deformation into the stick bore hole. The sticks were then, packaged in film, placed into a carton. The film was formed in such a manner that the sticks can be removed and transferred to the magazine of the automatic stuffing machine by the consumer without risk of breaking.

EXAMPLE 2

[0043] Example 1 was repeated except that instead of the easy-peel solution described there a liquid smoke preparation of 38% acidic liquid smoke (® Enviro 24 P from Red Arrow, Manitowoc, Wisconsin),  1% lecithin,  1% chromium-fatty acid complex (® Montacell), 10% glycerol and 50% water

[0044] was used. The impregnation produced therewith ensured ready peelability and at the same time had the effect that the smoking aroma transferred to the surface of the sausage emulsion. The stick broke at a load of 1 420 g.

EXAMPLE 3

[0045] A cellulose gel tube was produced according to example 1, but this time without an internal preparation. The casing was dried to 8 to 10% residual moisture.

[0046] After intermediate storage in a climatically controlled chamber the tube was taken off from the roll and shirred. During this, an aqueous solution of 10.0% lecithin, 33.0% propane-1,2-diol, 0.4% polyoxyethylene sorbitan monooleate (® Tween 80) 0.2% polyethylene glycol monoalkyl ether (® Genapol X 80) (HO—[CH₂—CH₂—O]_(n)—[CH₂]_(m)—CH₃, where on average n = 8 and m = 12), 12.5% silicone oil dispersion, 3.0% wheat protein (® Amypro SWP), 2.5% polytetrafluoroethylene dispersion and 38.4% water

[0047] was sprayed via the shirring mandrel onto the inside of the casing. The composition was selected so that at the desired surface concentration of the active compounds the stick had a moisture of 16 to 18%. The following steps, end closure and packaging were performed as in example 1. The stick withstood a load of 1 350 g.

EXAMPLE 4

[0048] Example 3 was repeated except that instead of the aqueous composition described there, a solution of 37.7% liquid smoke (® Zesti Smoke Code 10), 4.3% NaOH, 1.8% alginate, 10.1% lecithin, 3.0% ® Genapol and 43.1% water

[0049] was sprayed on. The impregnation, in addition to the easy-peel effect, simultaneously produced a finish having smoked aroma. The stick could be loaded up to 1 250 g. 

1. A stick of a tubular food casing based on cellulose characterized in that the casing is produced by the NMMO process.
 2. The stick as claimed in claim 1, characterized in that the casing has been transversely stretched by blow molding in the air section between annular die and surface of the spinning bath.
 3. The stick as claimed in claim 1 or 2, characterized in that the cellulose has a mean degree of polymerization DP of 300 to 700, preferably 400 to
 650. 4. The stick as claimed in one or more of claims 1 to 3, characterized in that the casing comprises up to 25% by weight, based on the weight of the cellulose, of further high-molecular-weight, slightly polar compounds.
 5. The stick as claimed in claim 4, characterized in that the further high-molecular-weight, slightly polar compound is a synthetic polymer or copolymer.
 6. The stick as claimed in one or more of claims 1 to 5, characterized in that the casing has a nominal caliber of 14 to 50 mm, preferably 16 to 25 mm.
 7. The casing as claimed in one or more of claims 1 to 6, characterized in that it comprises about 30 to 70 m, preferably about 40 to 60 m, of the casing.
 8. The stick as claimed in one or more of claims 1 to 7, characterized in that the casing comprises 8 to 20% by weight, preferably 16 to 18% by weight, of water.
 9. The stick as claimed in one or more of claims 1 to 8, characterized in that the casing comprises a plasticizer, preferably glycerol.
 10. The stick as claimed in one or more of claims 1 to 9, characterized in that the casing is provided with an impregnation or coating on the outside and/or on the inside.
 11. The stick as claimed in one or more of claims 1 to 10, characterized in that it is provided with an end closure.
 12. The stick as claimed in one or more of claims 1 to 11, characterized in that the ζ potential in the pH range from 6 to 10.5 is about −5 to −25 mV, and in the pH range from 3.5 to 5.5 is about +18 to −15 mV.
 13. The use of the stick as claimed in one or more of claims 1 to 12 on a stuffing apparatus in the production of cooked-meat sausages or scalded-emulsion sausages, preferably in the production of small sausages. 